 /*******************************************************************************
  * Copyright (c) 2005, 2006 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/

 package org.eclipse.ui.internal.operations;

 import org.eclipse.core.commands.operations.DefaultOperationHistory;
 import org.eclipse.core.commands.operations.IOperationApprover;
 import org.eclipse.core.commands.operations.IOperationHistory;
 import org.eclipse.core.commands.operations.IUndoContext;
 import org.eclipse.core.commands.operations.ObjectUndoContext;
 import org.eclipse.core.commands.operations.OperationHistoryFactory;
 import org.eclipse.ui.PlatformUI;
 import org.eclipse.ui.internal.misc.Policy;
 import org.eclipse.ui.operations.IWorkbenchOperationSupport;

 /**
  * <p>
  * Provides undoable operation support for the workbench. This includes providing access to the default
  * operation history and installing a workbench-specific operation approver that enforces a linear
  * undo strategy.
  * </p>
  *
  * @since 3.1
  */
 public class WorkbenchOperationSupport implements IWorkbenchOperationSupport {

     private ObjectUndoContext undoContext;
     private IOperationApprover approver;
     
     // initialize debug options
 static {
         DefaultOperationHistory.DEBUG_OPERATION_HISTORY_UNEXPECTED = Policy.DEBUG_OPERATIONS;
         DefaultOperationHistory.DEBUG_OPERATION_HISTORY_OPENOPERATION = Policy.DEBUG_OPERATIONS;
         DefaultOperationHistory.DEBUG_OPERATION_HISTORY_APPROVAL = Policy.DEBUG_OPERATIONS;
         DefaultOperationHistory.DEBUG_OPERATION_HISTORY_NOTIFICATION = Policy.DEBUG_OPERATIONS && Policy.DEBUG_OPERATIONS_VERBOSE;
         DefaultOperationHistory.DEBUG_OPERATION_HISTORY_DISPOSE = Policy.DEBUG_OPERATIONS && Policy.DEBUG_OPERATIONS_VERBOSE;
     }

     /**
      * Disposes of anything created by the operation support.
      */
     public void dispose() {
         /*
          * uninstall the operation approver that we added to the operation history
          */
         getOperationHistory().removeOperationApprover(approver);
         /*
          * dispose of all operations using our context
          */
         getOperationHistory().dispose(getUndoContext(), true, true, true);
     }

     /**
      * Returns the undo context for workbench operations.
      * The workbench configures an undo context with the appropriate policies
      * for the workbench undo model.
      *
      * @return the workbench operation context.
      * @since 3.1
      */
     public IUndoContext getUndoContext() {
         if (undoContext == null) {
             undoContext = new ObjectUndoContext(PlatformUI.getWorkbench(),
                     "Workbench Context"); //$NON-NLS-1$
 }
         return undoContext;
     }

     /**
      * Returns the workbench operation history.
      *
      * @return the operation history for workbench operations.
      * @since 3.1
      */
     public IOperationHistory getOperationHistory() {
         IOperationHistory history = OperationHistoryFactory.getOperationHistory();
         /*
          * Set up the history if we have not done so before.
          */
         if (approver == null) {
             /*
              * install an operation approver that prevents linear undo violations
              * in any context
              */
             approver = new AdvancedValidationUserApprover(getUndoContext());
             history.addOperationApprover(approver);
             /*
              * set a limit for the workbench undo context
              */
             history.setLimit(getUndoContext(), 25);
         }
         return history;
     }

 }

